WO2019196182A1

WO2019196182A1 - Magnesium oxide whisker in-situ synthesis spinel-reinforced magnesium oxide-based crucible and preparation method therefor

Info

Publication number: WO2019196182A1
Application number: PCT/CN2018/089573
Authority: WO
Inventors: 刘子利; 刘希琴; 叶兵; 丁之光; 丁文江
Original assignee: 凤阳爱尔思轻合金精密成型有限公司; 南京航空航天大学
Priority date: 2018-04-08
Filing date: 2018-06-01
Publication date: 2019-10-17
Also published as: CN108424124B; CN108424124A

Abstract

A magnesium oxide whisker in-situ synthesis spinel-reinforced magnesium oxide-based crucible that may perform sintering at a low temperature and that has excellent chemical stability and thermal shock resistance, and a preparation method therefor, the preparation method comprising the following steps: (1) according to mass percentage, mixing 15%-25% of nano alumina sol and 0.8%-1.5% of a rheological agent, the rest being magnesium oxide ceramic powder containing a nano titanium dioxide sintering aid, adding anhydrous ethanol, mixing evenly by means of ball milling, and then preparing a ceramic slurry having a solid content of 65%-75%; (2) preparing a crucible biscuit; (3) preparing a crucible blank; (4) placing the magnesium oxide-based crucible blank in alumina sol for vacuum impregnation treatment, then performing surface finishing treatment, drying, then performing high-temperature secondary sintering at a temperature of 1350°C-1550°C, and cooling to room temperature in the furnace to obtain a magnesium oxide-based crucible.

Description

In-situ synthesis of spinel reinforced magnesium oxide base by magnesium oxide whisker and preparation method thereof

Technical field

The invention relates to a magnesia-based crucible and a preparation method thereof, in particular to a magnesium oxide whisker in-situ synthesis of a spinel-reinforced magnesia-based crucible and a preparation method thereof, and belongs to the field of metal materials and metallurgy. The magnesium oxide based ruthenium prepared by the invention is particularly suitable for the smelting of magnesium and its alloys.

Background technique

In recent years, the demand for light weight has enabled the rapid development of magnesium alloy and aluminum alloy applications. Whether it is wrought magnesium, aluminum alloy or cast magnesium, aluminum alloy production is inseparable from the melting equipment. Magnesium is chemically active and easily reacts with oxygen, nitrogen and water vapor. It is easily oxidized and burned during melting and refining, and the resulting product remains in magnesium, which deteriorates the internal quality and performance of the product. The furnace is continuously smelted. When the molten alloy liquid is not in contact with the flame, the alloy element has low oxidation loss. Therefore, although the furnace melting is limited by the capacity of the crucible, it is still a commonly used equipment for melting the magnesium alloy. For aluminum alloys, in addition to large-scale reversing furnaces, large-scale remanufacturing furnaces are still the main equipment for small and medium-sized foundry companies to cast aluminum alloys.

坩埚 is the key to determining the quality of smelting. The metal smelting used in industrial applications is mainly iron enamel (such as cast iron, stainless steel) and non-metal bismuth. Iron bismuth (carbon steel, stainless steel, etc.) is a commonly used crucible for magnesium and aluminum alloy casting, but molten alloy liquid and liquid flux are easily corroded during heating to reduce its service life, and iron easily enters molten alloy. Contaminant alloy in liquid. In non-metal bismuth, the strength of graphite crucible is low, the crucible is easily broken when it is improperly operated or unevenly heated, and the thermal conductivity is remarkably lowered after a long period of use. Therefore, graphite crucible is rarely used at present.

The application of ceramic crucibles has greatly promoted the development of special smelting in the metallurgical industry, especially nuclear materials. Magnesium alloy smelting adopts ceramic enamel or ceramic lining to avoid the use of iron lanthanum in the magnesium alloy casting process to mix harmful elements such as Fe, Cu, Cr, etc., and improve the corrosion resistance of magnesium alloy products. Although the melting temperature of magnesium alloy is not high (similar to aluminum alloy, about 700 °C), the chemical properties of magnesium alloy are very active, the standard formation of MgO is very low, and it is easily oxidized during the smelting process, resulting in loose magnesia. The melt cannot be protected and the heat generated accelerates the oxidative combustion; on the other hand, the vapor pressure of magnesium is quite high (1037 Pa at 727 ° C), and the magnesium alloy liquid and vapor easily penetrate into the interior of the porous ceramic material. The reaction, the reaction product and the ceramic matrix have different physical properties such as thermal expansion coefficient and elastic modulus, and tend to generate stress to cause the reaction product to fall off from the ceramic matrix, resulting in deterioration of the ceramic, loose structure and damage, and contamination of the alloy melt, such as high activity. The magnesium melt is very easy to react with the widely used Al ₂ O ₃ , ZrO ₂ , SiC, SiO ₂ ceramic matrix tantalum materials (1) to (4) to rapidly damage and contaminate the magnesium alloy melt. magnesium alloy melting ceramic material with more demanding requirements, the conventional _{_{_{Al 2 O 3, ZrO 2,}}} SiC, SiO 2 based ceramic crucible is not suitable for magnesium alloys and cast magnesium, magnesium alloy on Melting with fewer reports of ceramic materials.

3Mg _(l) +Al ₂ O _3(s) =3MgO _(s) +2Al _(l) (1)

2Mg(l)+ZrO ₂ (s)=2MgO(s)+Zr(s) (2)

6Mg(l)+4Al(l)+3SiC(s)=3Mg ₂ Si(s)+Al ₄ C ₃ (s) (3)

4Mg(l)+SiO ₂ (s)=2MgO(s)+Mg ₂ Si(s) (4)

MgO is a cubic crystal NaCl structure with a lattice constant of 0.411 nm. It is an ion-bond compound with a melting point of 2852 ° C, which is much higher than the commonly used Al ₂ O ₃ (2054 ° C) and SiO ₂ (1650 ± 50 ° C). Therefore, magnesium oxide products have good chemical stability, high electrical resistivity and strong corrosion resistance to metals, slag and alkaline solutions. Compared with commonly used ceramic materials, MgO has good high-temperature chemical stability with magnesium and its alloy melts. Its use temperature is as high as 1600-1850 °C, and the flux slag composed of molten chloride salt and fluorate does not occur. The reaction is mixed with the flux and has a small wetting angle to easily adsorb the flux inclusions in the magnesium melt. Therefore, the MgO ceramic crucible is an ideal choice for the smelting and purifying of the magnesium alloy liquid. In addition, dense MgO ceramics are also considered to be preferred smelting vessel materials for smelting high purity iron and its alloys as well as nickel, uranium, thorium, zinc, tin, aluminum and their alloys.

Burning below the melting point of the oxide composition is the most critical step necessary to prepare the ceramic material, and the sintering, grain growth and other processes occurring at high temperatures determine the microstructure of the ceramic material. And performance. Chinese patent document CN103030407B (a preparation method of high-strength, high-density, high-purity magnesium oxide bismuth), Chinese patent document CN1011306B (pure magnesium oxide foam ceramic filter and preparation process thereof), etc. Ceramics, because MgO has a high melting point and a high coefficient of thermal expansion (13.5 × 10 ^-6 / ° C), it causes difficulty in sintering (sintering temperature is not less than 0.8 times its melting point) and thermal shock resistance is poor, limiting The application and development of MgO ceramics.

The research shows that the heat loss per unit product is reduced by more than 10% for each reduction of the firing temperature in the sintering ceramics. The addition of sintering aid is an important technical means to reduce the sintering temperature of MgO ceramics. When V ₂ O ₅ powder is added, MgO forms a liquid phase of approximately Mg ₃ V ₂ O ₈ with V ₂ O ₅ at 1190 ° C, promotes sintering, and can significantly reduce the sintering temperature of MgO foam ceramic, but V ₂ O ₅ has a detrimental effect on the respiratory system and skin during use, and has strict restrictions on operation. Like V ₂ O ₅ , cobalt oxide is also a good low-temperature sintering aid, but it is also limited as a highly toxic substance and a rare resource. Chinese patent document CN100434390C (composition for making ruthenium and method thereof), CN101785944B (preparation method for magnesium oxide foam ceramic filter for magnesium and magnesium melt filtration), adding fluorite (melting point 1423 ° C) and magnesium fluoride ( Melting point 1248 ° C), the solid solution of fluoride in the sintering process not only increases the lattice distortion of the matrix magnesium oxide, but also easily forms a low melting point liquid phase, thereby reducing the sintering temperature of the magnesium oxide ceramic; however, during the sintering process The combination of F in fluoride with Si, Al, Fe and Ca, most of which (about 70% in tile production) volatilizes in gaseous form, not only erodes the body itself but damages the quality of the sintered ceramics, and more seriously discharges to Fluoride pollution can occur in the atmosphere. Fluoride can enter the human body through the respiratory tract, digestive tract and skin. It has toxic effects on the central nervous system and myocardium. Low concentration of fluorine pollution can lead to brittle calcification of teeth and bones. "(GB25464-2010) in a predetermined discharge standards fluoride must be less than 5.0mg / m ^3, to magnesium fluoride as a low-temperature ceramic sintering aid will increase the gaseous fluorides Putting and increasing the burden of environmental protection; in addition, the fluoride ion in the solid solution fluoride remaining in the ceramic is in the form of replacing oxygen ions, which causes the chemical stability of the intergranular bond to decrease, and it is difficult to resist the long time of the flux in the magnesium melt. erosion. The preparation of the foam ceramic filter disclosed in the Chinese patent document CN104496492B (a composite magnesium carbon refractory crucible and a preparation method thereof) uses a silica sol or the like as a binder, and the presence of a SiO ₂ component between the sintered ceramic particles enables It is easy to react with magnesium and its alloy melt according to formula (4), which also reduces the chemical stability of the ceramic. Chinese patent document CN100536986C (magnesia foam ceramic filter), CN103553686A (a magnesium aluminum spinel foam ceramic filter and its preparation method) and other patent documents, boron trioxide and borax as the low temperature of magnesium oxide ceramics The sintering aid forms a liquid phase when the boron trioxide is higher than 450 ° C. When the sintering temperature exceeds 1350 ° C, the reaction with magnesium oxide forms magnesium borate in the form of a liquid phase to lower the sintering temperature. However, boron trioxide is easily reacted with magnesium and aluminum, and is unstable in the melt of magnesium and aluminum alloy. Meanwhile, since boron trioxide is dissolved in a solvent such as water and ethanol, it can strongly absorb water to form boric acid in the air. The boron trioxide added during the preparation of the ceramic product is dissolved in water to form an aqueous boric acid solution, which is easily reacted with magnesium oxide to form a magnesium borate precipitate to reduce its effect. Gallium oxide is a homologous oxide of boron trioxide, which forms a spinel-type MgGa ₂ O ₄ with magnesium oxide at a lower temperature to reduce the sintering temperature, but has a small amount of gallium resources (gallium is a strategy). Reserve metals), the higher price of gallium oxide limits its use in ordinary ceramics.

Ceramic enamel industry production methods In addition to small 坩埚 using dry pressing method, grouting and isostatic pressing are two common preparation techniques. Although the isostatic pressing has the advantages of high density and high yield, and the bismuth body is not easily deformed during the sintering process, it is found that the isostatic pressing machine has high cost, low efficiency, poor thermal stability, rapid heating and During the cooling process, cracking and spalling are likely to occur, and the life is short. Grouting is the most reasonable method for niobium or other hollow products. Under the same conditions, grouting can obtain larger bulk density of greens than other forming methods (more than 2000kg/cm ³ molding). The product under pressure is also dense and the firing temperature required is also low.

Summary of the invention

The object of the present invention is to provide a preparation method of in-situ synthesis of spinel-reinforced magnesia-based bismuth by magnesium oxide whisker which is excellent in chemical stability and thermal shock resistance which can be sintered at a low temperature.

In order to achieve the above technical purpose, the technical solution of the present invention is:

A magnesium oxide whisker in-situ synthesis of spinel-enhanced magnesia-based bismuth, and a light-burned magnesia ceramic slurry containing nano-iron oxide, nano-zinc oxide and magnesium oxide whisker is grouted in a plaster mold and dried And obtained by sintering.

A preparation method of in-situ synthesis of spinel-enhanced magnesium oxide based on magnesium oxide whisker, comprising the following steps:

(1) According to the mass percentage, 15% to 25% nano-alumina sol, 0.8% to 1.5% rheological agent, and the rest are magnesium oxide ceramic powder containing nano-titanium dioxide sintering aid, and then added with anhydrous ethanol. A ceramic slurry having a solid content of 65% to 75% is prepared.

The added nano-alumina sol not only forms a γ-Al ₂ O ₃ coating film on the surface of the lightly burned magnesium oxide particles and the highly uniformly dispersed nano-Fe ₂ O ₃ powder and the magnesium oxide whisker, but acts as a binder. In the sintering process, Al ₂ O ₃ and Fe ₂ O ₃ together with MgO in-situ synthesis of MA-MF composite spinel solid solution phase which is chemically stable to magnesium and its alloy melt, avoiding the addition of existing products to silica sol, The binder such as ethyl silicate damages the chemical stability of the ceramic; at the same time, the ceramic component does not contain sodium salt (if carboxymethyl cellulose sodium is not used in the rheological agent), the residual ionic radius is avoided. Large Na ⁺ hinders the sintering of ceramics.

The nano aluminum sol has a solid content of 20% to 25% and a pH of ≥4.

The rheological agent is a mixture of polyvinyl butyral and a cellulose ether, wherein the polyvinyl butyral is 50% by mass of the rheology agent, and the cellulose ether is an industrial hydroxypropyl methyl group. One of cellulose and hydroxyethyl cellulose or a mixture thereof.

Cellulose ether and polyvinyl butyral are not only good dispersing agents for nano-iron oxide, nano-zinc oxide powder and magnesium oxide whisker, but also prevent agglomeration of the slurry, and can bond when preparing the green body. The action of the agent gives the green body a higher strength while being easily escaping during the sintering process without contaminating the product.

The ceramic powder is a mixture of nano iron oxide, nano zinc oxide, magnesium oxide whisker and light burned magnesium oxide. The nanometer iron oxide accounts for 1% to 2% of the mass of the ceramic powder, the nano zinc oxide accounts for 0.5% to 1% of the mass of the ceramic powder, and the magnesium oxide whisker accounts for 1.5% to 2.5 of the mass of the ceramic powder. %, the rest is light burned magnesia. The nanometer iron oxide has a particle diameter of 30 nm to 60 nm, the nano zinc oxide has a particle diameter of 20 nm to 30 nm, and the magnesium oxide whisker is an industrial product having a diameter of 2 μm to 5 μm and a length of 200 μm to 1000 μm. The light-burned magnesium oxide powder has a particle diameter of 250 mesh to 500 mesh (median diameter d ₅₀ is 58 μm).

The light-burned magnesia powder has high sintering activity. The nano-alumina sol and nano-iron oxide can be dissolved into the lattice of MgO during the sintering process to cause lattice distortion of the MgO crystal, activate the crystal lattice, and pass through The reaction is sintered with MgO particles and magnesium oxide whiskers to form a MA-MF composite spinel phase, thereby promoting sintering and particle phase bonding. On the other hand, the nano-powder has the characteristics of large specific surface area, high surface energy and high activity. The low-temperature sintering aid is added in the form of nano-alumina sol and nano-iron oxide to optimize the gradation and mixing uniformity of the ceramic particles, and the nano-powder Due to its own surface and interface effects, the sufficient contact between the nano-sintering aid and the MgO particles and the magnesium oxide whisker causes the reaction rate of the spinel phase to increase rapidly, thereby further reducing the sintering temperature and lowering the sintering temperature. Conducive to reducing energy consumption and production costs.

The solid phase component of the aluminum sol is highly active porous γ-Al ₂ O ₃ , which has the same crystal structure as the magnesium aluminate spinel MA. The use of fibers and whiskers as reinforcements can improve the mechanical properties of ceramic matrix composites. Whisker refers to a single crystal fiber material having a length ratio (generally greater than 10) and an area of 5.2 x 10 ^-4 cm ² . Magnesium oxide whiskers have a high melting point (2850 ° C), high strength, and high modulus of elasticity. In the solution provided by the present invention, the nano zinc oxide plays a role of promoting densification in sintering; the high sintering activity of the lightly burned magnesium oxide particles and the highly dispersed magnesium oxide whisker surface are surrounded by the nano aluminum sol film, and The in-situ reaction during the sintering process produces a magnesium-aluminum spinel MA phase. The solubility of iron in periclase MgO is much greater than that of aluminum. The effective solubility of Fe ₂ O ₃ and Al ₂ O ₃ in periclase at 1600 ° C is about 60% and 1%, respectively. Adding nano-Fe ₂ O ₃ , Fe ³⁺ diffuses rapidly into MgO, makes spinel MgO spinel petrochemical, and promotes the diffusion of Al ₂ O ₃ into MgO. Therefore, the MA generated by in-situ reaction There is a close continuous bonding interface between MF and periclase solid solution. Since MA and MF are mutually soluble, the MgO particles are directly combined with the surrounding MA-MF composite spinel, and the pinning of the composite spinel phase inhibits the growth of the magnesium oxide particles, thereby refining the ceramic structure. And the density between the ceramic grains is increased; at the same time, the morphology of the magnesium oxide whiskers having a certain directionality in the formed green body is inherited by the formed magnesium aluminum spinel phase.

The ceramic slurry is prepared by adding a lightly burned magnesium oxide powder to a ball mill tank according to a ratio, and the nano aluminum sol, nano iron oxide, nano zinc oxide, magnesium oxide whisker, rheological agent and absolute ethanol. After mixing and sonicating for 30 min to 60 min, the nano-iron oxide, nano-zinc oxide and magnesia whiskers are fully dispersed and added to the ball-milling tank, and then the corundum balls are added in a ratio of 2:1 of the ball to the ball, and the ball is milled at 60-120 rpm. The mixture was uniformly obtained from 2 h to 4 h.

(2) The ceramic slurry is poured into a gypsum mold by a grouting method, demolded, and the ethanol solvent is removed in a ventilating chamber at 40 ° C to 50 ° C to obtain a sapphire slab.

The preparation method of the bismuth blank is: rapidly injecting the ceramic slurry into the plaster mold, and placing it on the vibration molding machine to form a vibration. When the slurry is completely filled into the mold, the surface of the slurry is uniformly sprayed, the vibration is stopped, and the surface of the slurry is smoothed. The mold body is demolded when no ethanol liquid escapes, and is obtained by removing the ethanol solvent in a ventilating chamber at 40 ° C to 50 ° C.

(3) The dried alfalfa blank is placed in a sintering furnace, heated to a temperature of 1350 ° C to 1550 ° C for high-temperature sintering, and cooled to room temperature to obtain a magnesia-based niobium blank.

The high-temperature sintering process of the magnesium oxide-based ruthenium blank is: heating to 550 ° C at a temperature increase rate of 60 ° C / h, and decomposing and vaporizing the organic matter (rheology agent, etc.) in the green body to be heated at 200 ° C / h The temperature is heated to a temperature of 1100 ° C, and then heated to a temperature of 1350 ° C to 1550 ° C at a heating rate of 50 ° C / h, and kept at this temperature for 2 to 3 h.

(4) The magnesium oxide based ruthenium blank is vacuum impregnated in an aluminum sol, and then subjected to surface buffing treatment. After drying, it is subjected to high temperature secondary sintering at a temperature of 1350 ° C to 1550 ° C, and is oxidized by cooling to room temperature with the furnace. Magnesium based bismuth.

The vacuum impregnation treatment method of the magnesium oxide based ruthenium blank in the aluminum sol is: placing the magnesium oxide based ruthenium blank in an aluminum sol, vacuum infiltration treatment under a negative pressure of 0.02 MPa to 0.05 MPa for 30 min, at 120 ° C After baking in an oven at ±10 ° C for 24 hours, it was repeated twice as described above; then surface-polishing with an aluminum sol as a cooling liquid on a grinding machine, and baking in an oven at 120 ° C ± 10 ° C for 24 hours. Finally, the surface-polished dried ram is subjected to high-temperature secondary sintering, which is heated to 1100 ° C at a heating rate of 200 ° C / h, and then heated to 1350 ° C at a heating rate of 50 ° C / h ~ 1550 ° C, and kept at this temperature for 2 ~ 3h.

The lower heating rate in the low-temperature sintering stage can prevent the decomposition rate of the rheological agent from being too fast, leading to collapse or deformation damage of the green body. After the sintering temperature exceeds 1100 ° C in the high-temperature sintering stage, the lower heating rate can ensure the uniform temperature in the sintered body. At the same time, the formation speed of the spinel is prevented from being uniform and the phase transformation stress generated too quickly is prevented from causing deformation and cracking of the sintered body.

The magnesium oxide based bismuth of the invention adopts a grouting preparation preparation method, and has the advantages of simple process equipment, uniform wall thickness, low cost, high efficiency, and suitable for large-scale production; the prepared magnesium oxide whisker is synthesized in situ by spinel reinforcement. Magnesium oxide based bismuth does not contain any components which reduce its chemical stability. The added nano-alumina sol and nano-iron oxide can not only reduce the sintering temperature, but also highly uniformly disperse into the magnesium oxide ceramic powder particles and The reaction forms a spinel solid solution phase which is chemically stable to the melt of magnesium and its alloy, and the magnesium oxide particles are welded together, and the morphology of the magnesium oxide whisker having a certain orientation is formed by the magnesium aluminate spinel phase formed. Inheritance, nano zinc oxide plays a role in promoting densification during sintering. Therefore, the prepared magnesium oxide base has good strength, chemical stability and thermal shock resistance, and is particularly suitable for the melting of magnesium and aluminum alloy. Specifically:

1. The in-situ synthesis of spinel-enhanced magnesium oxide based on the magnesium oxide whiskers of the present invention has excellent chemical stability. Compared with Al ₂ O ₃ and Cr ₂ O ₃ , Fe ₂ O ₃ has the highest solid solubility in the sodal magnesia MgO phase. The added nano Fe ₂ O _{3 is} easily dissolved in the MgO phase to form a magnesium iron spinel (MgFe ₂ O ₄ , MF) phase (melting point 2030 ° C) having high temperature stability. Although the raw material aluminum sol component contains γ-Al ₂ O ₃ reacted with the magnesium liquid, the added nano aluminum sol is in the surface of the lightly burned magnesium oxide particles and the highly uniformly dispersed nano Fe ₂ O ₃ powder and the magnesium oxide whisker Forming a γ-Al ₂ O ₃ coating film, in which γ-Al ₂ O ₃ and lightly burned MgO particles in the aluminum sol react in situ with magnesium oxide whiskers to form a high melting point magnesium aluminum having a face centered cubic lattice during sintering Spinel (MgAl ₂ O ₄ , MA) phase (melting point 2135 ° C). MA and MF can be completely miscible. According to the results of XRD analysis, the sintered strontium prepared by the present invention has only the periclase MgO and MA-MF composite spinel solid solution phase.

In the reaction system of the magnesium melt and the alumina-added MgO-Al ₂ O ₃ sintered ceramic, in addition to the reaction formula (1), the following reaction may exist:

3Mg _(l) +4Al ₂ O _3(s) =3MgAl ₂ O _4(s) +2Al _(l) (5)

The reaction between alumina and magnesia to form magnesium aluminum spinel MgAl ₂ O ₄ is:

MgO _(s) +Al ₂ O _3(s) =MgAl ₂ O _4(s) (6)

The reaction of the magnesium melt with the magnesium aluminate spinel MgAl ₂ O ₄ is:

3Mg _(l) +MgAl ₂ O _4(s) =2Al _(l) +4MgO _(s) (7)

According to the Handbook of Pure Chemical Thermochemistry Data (edited by Ihsan Barron, translated by Cheng Nailiang, Beijing: Science Press, 2003), the substance of the reaction system of magnesium melt and magnesium aluminate spinel at 900-1200K The calculation results of Gibbs free energy data and Gibbs free energy changes ΔG ₁ , ΔG ₅ , ΔG ₆ , ΔG ₇ of reactions (1), 5), (6) and (7) are shown in Table 1.

Table 1 Calculation results of Gibbs free energy change ΔG for each reaction in 900-1200K magnesium melt and magnesium aluminum spinel reaction system

The Gibbs free energy ΔG _{5 of the} formula (5) of the reactive magnesium melt and the alumina-forming magnesium aluminate spinel is the smallest at different temperatures, indicating that the reaction takes precedence at the usual melting temperature of the magnesium alloy. The reaction formula (7) of magnesium liquid and magnesium aluminum spinel is thermodynamically achievable, but the reaction is essentially a reaction between the magnesium solution and the decomposition product of magnesium aluminate spinel, but it is known from Table 1. At the melting temperature of magnesium alloy, the reaction of magnesium aluminate spinel into alumina and magnesia is difficult to carry out (reaction of reaction formula (6)), and the residual alumina in the sintered ceramic is also preferred to magnesium. Magnesium-aluminum spinel is formed according to reaction formula (5); on the other hand, the MgO side of the MgO-Al ₂ O ₃ phase diagram is a eutectic phase diagram of the periclase solid solution and the MA spinel solid solution, which is generated in situ by reaction. There is almost no O ^2- diffusion in the MA process. Only Mg ²⁺ and Al ³⁺ diffuse through the fixed oxygen lattice. The rate of formation is determined by the slower diffusion of Al ³⁺ , and the MA phase is mainly in Al ₂ O ₃ . The side is formed by the internal growth method, resulting in the formation of a finite solid solution between the MA phase and the MgO, while the MgO content in the outer layer of the MA in contact with the MgO particles is much higher than the average value, and the MgO does not react with the magnesium melt, therefore, The magnesium-aluminum spinel phase in which the magnesia particles are fused together in the sintered ceramic structure is capable of being in the magnesium melt Stable enough.

The in-situ synthesis of the spinel-enhanced magnesium oxide based on the magnesium oxide whisker of the present invention does not contain any component which reduces its chemical stability, and the added nano-alumina sol is not only in the light-burned magnesium oxide particles but also in highly uniformly dispersed nanometers. Fe ₂ O ₃ powder and magnesium oxide whisker form a γ-Al ₂ O ₃ coating film to act as a binder. In the sintering process, Al ₂ O _{3 is} combined with Fe ₂ O ₃ and MgO in situ. MA-MF composite spinel solid solution phase with chemical stability to magnesium and its alloy melt, avoiding the damage of chemical stability of ceramics by adding silica sol, ethyl silicate and other binders to existing products; The component also does not contain sodium salt (such as sodium carboxymethyl cellulose is not used in the rheological agent), which avoids the inhibition of ceramic sintering by Na ⁺ with a large residual ionic radius.

Since the reaction formulas (1) and (5) can be spontaneously carried out at the usual melting temperatures of magnesium alloys, the melting temperatures of aluminum and its alloys are the same as those of magnesium and its alloys, MgO and MA spinel phases and aluminum and The alloy melt does not undergo the reverse reaction of the reaction formulas (1) and (5); it is the same as that used for the melt of magnesium and its alloy, avoiding the addition of binders such as silica sol and ethyl silicate to ceramics in aluminum and its alloys. Damage to chemical stability in the melt (even if the material contains 1% SiO ₂ , the melt of aluminum and its alloy will react with Al + SiO ₂ → Al ₂ O ₃ + Si in SiO ₂ at high temperature) Therefore, the prepared magnesium oxide whisker in-situ synthesis of spinel-reinforced magnesium oxide-based cerium can also be used for the smelting purification of aluminum and its alloys. In addition, the grouting slurry for preparing crucible proposed by the present invention can also be used as a brick and inner wall smoothing paste for an aluminum alloy reflective melting furnace.

2. The in-situ synthesis of spinel-enhanced magnesium oxide based on the magnesium oxide whiskers of the present invention has good low-temperature sintering properties. The light-burned magnesia powder used in the invention has high sintering activity, and the nano-alumina sol and the nano-iron oxide can be solid-dissolved into the lattice of MgO during the sintering process to cause lattice distortion of the MgO crystal, and the activated lattice At the same time, a MA-MF composite spinel phase is formed by reaction with MgO particles and magnesium oxide whiskers, thereby promoting sintering and particle phase bonding. On the other hand, the nano-powder has the characteristics of large specific surface area, high surface energy and high activity. The low-temperature sintering aid is added in the form of nano-alumina sol and nano-iron oxide to optimize the gradation and mixing uniformity of the ceramic particles, and the nano-powder Due to its own surface and interface effects, the sufficient contact between the nano-sintering aid and the MgO particles and the magnesium oxide whisker causes the reaction rate of the spinel phase to increase rapidly, thereby further reducing the sintering temperature and lowering the sintering temperature. Conducive to reducing energy consumption and production costs. The test results show that the sintering temperature of in-situ synthesis of spinel-reinforced magnesium oxide based on magnesium oxide whiskers is only 1350 °C ~ 1550 °C.

3. The in-situ synthesis of spinel-enhanced magnesium oxide based on the magnesium oxide whiskers of the present invention has good thermal shock resistance. The solid phase component of the aluminum sol is highly active porous γ-Al ₂ O ₃ , which has the same crystal structure as the magnesium aluminate spinel MA. The use of fibers and whiskers as reinforcements can improve the mechanical properties of ceramic matrix composites. Whisker refers to a single crystal fiber material having a length ratio (generally greater than 10) and an area of 5.2 x 10 ^-4 cm ² . Magnesium oxide whiskers have a high melting point (2850 ° C), high strength, and high modulus of elasticity. In the solution provided by the present invention, the nano zinc oxide plays a role of promoting densification in sintering; the high sintering activity of the lightly burned magnesium oxide particles and the highly dispersed magnesium oxide whisker surface are surrounded by the nano aluminum sol film, and The in-situ reaction during the sintering process produces a magnesium-aluminum spinel MA phase. The solubility of iron in periclase MgO is much greater than that of aluminum. The effective solubility of Fe ₂ O ₃ and Al ₂ O ₃ in periclase at 1600 ° C is about 60% and 1%, respectively. Adding nano-Fe ₂ O ₃ , Fe ³⁺ diffuses rapidly into MgO, makes spinel MgO spinel petrochemical, and promotes the diffusion of Al ₂ O ₃ into MgO. Therefore, the MA generated by in-situ reaction There is a close continuous bonding interface between MF and periclase solid solution. Since MA and MF are mutually soluble, the MgO particles are directly combined with the surrounding MA-MF composite spinel, and the pinning of the composite spinel phase inhibits the growth of the magnesium oxide particles, thereby refining the ceramic structure. And the density between the ceramic grains is increased; at the same time, the morphology of the magnesium oxide whiskers having a certain directionality in the formed blank is inherited by the formed magnesium aluminum spinel phase, and therefore, the prepared magnesium oxide whiskers In-situ synthesis of spinel-enhanced magnesia-based niobium has higher mechanical properties, high temperature impact resistance and thermal shock resistance.

In addition, the cellulose ether and polyvinyl butyral as rheological agents in the preparation method of the present invention are not only good dispersants of nano iron oxide, nano zinc oxide powder and magnesium oxide whiskers, but also prevent agglomeration of the slurry. Moreover, when the green body is prepared, it can act as a binder to make the green body have higher strength, and at the same time, it is easy to escape during the sintering process without polluting the product, thereby ensuring the quality of the sintered concrete.

DRAWINGS

Figure 1 is a flow chart showing the preparation process of zirconia staple fiber and basic magnesium sulfate whisker composite reinforcing magnesium oxide based ruthenium.

detailed description

The present invention will be further described in detail below in conjunction with the drawings and specific embodiments.

Magnesium oxide whisker in-situ synthesis of spinel-enhanced magnesia-based bismuth, and light-burning magnesia ceramic slurry containing nano-iron oxide, nano-zinc oxide and magnesia whisker is grouted in a gypsum mold, dried and sintered get. The specific preparation process is shown in Figure 1.

Example 1

According to the nanometer iron oxide, the mass percentage of the ceramic powder is 1%, the nano zinc oxide is 0.5%, the magnesium oxide whisker is 1.5%, and the rest is the ratio of the light burned magnesium oxide, and the nanometer iron oxide and the particle having a particle diameter of 30 nm are used. Nano-zinc oxide having a diameter of 20 nm, commercial magnesium oxide whiskers (having a diameter of 2 μm to 5 μm and a length of 200 μm to 1000 μm) and a light-burned magnesium oxide powder having a particle diameter of 250 mesh (medium diameter d ₅₀ of 58 μm) are mixed and formulated. A ceramic powder; a rheological agent is prepared by mixing a ratio of polyvinyl butyral to hydroxypropyl methylcellulose in a mass ratio of 1:1.

According to the mass percentage, the nano-alumina sol with a solid content of 25% is 25% (selecting a near-neutral commercial nano-aluminum sol with a pH value, the same below), the rheological agent is 0.8%, and the rest is a ceramic powder for compounding. Firstly, the lightly burned magnesia powder is added to the ball mill tank according to the ratio, and the nano aluminum sol, the nano iron oxide, the nano zinc oxide, the magnesium oxide whisker, the rheological agent and the appropriate amount of absolute ethanol (according to the solidification of the ceramic slurry) The content of the content is determined, the same as below, mixed and sonicated for 30 minutes, the nano-iron oxide, nano-zinc oxide, magnesium oxide whisker is fully dispersed and added to the ball mill tank, and then the corundum ball is added according to the ratio of the ball to the ratio of 2:1. The mixture was ball milled at 60 rpm for 4 hours to be uniformly mixed to obtain a ceramic slurry having a solid content of 65%.

The ceramic slurry is quickly injected into the plaster mold and placed on a vibration molding machine to form a vibration. When the slurry is completely filled into the mold, the surface of the slurry is uniformly sprayed to stop the vibration and the surface of the slurry is smoothed. The mold body was demolded when no ethanol liquid escaped, and the ethanol solvent was removed in a ventilating chamber at 40 ° C to obtain a sapphire.

The dried green body is placed in a sintering furnace, heated to 550 ° C at a temperature increase rate of 60 ° C / h, and the organic matter such as a rheological agent in the green body is decomposed and vaporized, and heated to 1100 at a heating rate of 200 ° C / h. The temperature was °C, then heated to a temperature of 1550 ° C at a heating rate of 50 ° C / h, and held at this temperature for 2.5 h, and cooled to room temperature with a furnace to obtain a magnesia-based niobium blank.

The magnesium oxide based ruthenium blank is placed in an aluminum sol, vacuum impregnated at a vacuum of 0.02 MPa for 30 min, and baked in an oven at 120 ° C ± 10 ° C for 24 hours, and then repeated twice as described above; On the grinding machine, the surface is polished with aluminum sol as cooling liquid, and then baked in an oven at 120 °C ± 10 °C for 24 hours. Finally, the surface-polished dried enamel blank is subjected to high-temperature secondary sintering, and the secondary sintering process is The mixture was heated to 1,100 ° C at a heating rate of 200 ° C / h, then heated to 1550 ° C at a heating rate of 50 ° C / h, and held at this temperature for 2.5 h, and cooled to room temperature with a furnace to obtain a magnesia-based niobium blank.

Example 2

According to the nanometer iron oxide, the mass percentage of the ceramic powder is 2%, the nano zinc oxide is 1%, the magnesium oxide whisker is 2.5%, and the rest is the ratio of light burned magnesium oxide, and the nanometer iron oxide and the particle having a particle diameter of 60 nm are used. Nano-zinc oxide with a diameter of 30 nm, commercial magnesium oxide whiskers (with a diameter of 2 μm to 5 μm, length of 200 μm to 1000 μm) and light-burned magnesium oxide powder with a particle size of 500 mesh (medium diameter d ₅₀ of 25 μm) A ceramic powder; a rheological agent is prepared by mixing a ratio of polyvinyl butyral to hydroxypropyl methylcellulose in a mass ratio of 1:1.

According to the mass percentage, the nano-alumina sol with a solid content of 20% was 15%, the rheological agent was 1.5%, and the rest was made of ceramic powder. Firstly, the lightly burned magnesia powder is added to the ball mill tank according to the ratio, and the nano aluminum sol, the nano iron oxide, the nano zinc oxide, the magnesium oxide whisker, the rheological agent and the appropriate amount of absolute ethanol are mixed and sonicated for 30 minutes. The nano-iron oxide, nano-zinc oxide and magnesium oxide whiskers are fully dispersed and added to the ball-milling tank, and then the corundum balls are added in a ratio of 2:1 of the ball-to-ball ratio, and ball-milled at 120 rpm for 2 hours to obtain a solid content of 70%. Ceramic slurry.

The ceramic slurry is quickly injected into the plaster mold and placed on a vibration molding machine to form a vibration. When the slurry is completely filled into the mold, the surface of the slurry is uniformly sprayed to stop the vibration and the surface of the slurry is smoothed. The mold body was demolded when no ethanol liquid escaped, and the ethanol solvent was removed in a ventilating chamber at 50 ° C to obtain a sapphire.

The dried green body is placed in a sintering furnace, heated to 550 ° C at a temperature increase rate of 60 ° C / h, and the organic matter such as a rheological agent in the green body is decomposed and vaporized, and heated to 1100 at a heating rate of 200 ° C / h. The temperature was °C, then heated to a temperature of 1350 ° C at a heating rate of 50 ° C / h, and kept at this temperature for 3 h, and cooled to room temperature with a furnace to obtain a magnesia-based niobium blank.

The magnesium oxide based ruthenium blank is placed in an aluminum sol, vacuum impregnated for 30 min under a vacuum of 0.05 MPa, and baked in an oven at 120 ° C ± 10 ° C for 24 hours, and then repeated twice as described above; On the grinding machine, the surface is polished with aluminum sol as cooling liquid, and then baked in an oven at 120 °C ± 10 °C for 24 hours. Finally, the surface-polished dried enamel blank is subjected to high-temperature secondary sintering, and the secondary sintering process is The mixture was heated to 1,100 ° C at a heating rate of 200 ° C / h, then heated to 1350 ° C at a heating rate of 50 ° C / h, and kept at this temperature for 3 h, and cooled to room temperature with a furnace to obtain a magnesia-based niobium blank.

Example 3

According to the nanometer iron oxide, the mass percentage of the ceramic powder is 1.5%, the nano zinc oxide is 0.75%, the magnesium oxide whisker is 2%, and the rest is the proportion of light burned magnesium oxide, and the nanometer iron oxide and the particle having a particle diameter of 50 nm are used. Nano-zinc oxide with a diameter of 25 nm, commercial magnesium oxide whiskers (with a diameter of 2 μm to 5 μm, length of 200 μm to 1000 μm) and light-burned magnesium oxide powder with a particle size of 325 mesh (medium diameter d ₅₀ of 45 μm) A ceramic powder; a rheological agent is prepared by mixing a mass ratio of polyvinyl butyral to hydroxyethyl methyl cellulose of 1:1.

According to the mass percentage, the nano-alumina sol with a solid content of 22% was 20%, the rheological agent was 1.0%, and the rest was made of ceramic powder. Firstly, the lightly burned magnesia powder is added to the ball mill tank according to the ratio, and the nano aluminum sol, the nano iron oxide, the nano zinc oxide, the magnesium oxide whisker, the rheological agent and the appropriate amount of absolute ethanol (according to the solidification of the ceramic slurry) The content of the content is determined, the same as below, mixed and sonicated for 30 minutes, the nano-iron oxide, nano-zinc oxide, magnesium oxide whisker is fully dispersed and added to the ball mill tank, and then the corundum ball is added according to the ratio of the ball to the ratio of 2:1. After ball milling for 3 h at 90 rpm, the mixture was uniformly mixed to obtain a ceramic slurry having a solid content of 75%.

The ceramic slurry is quickly injected into the plaster mold and placed on a vibration molding machine to form a vibration. When the slurry is completely filled into the mold, the surface of the slurry is uniformly sprayed to stop the vibration and the surface of the slurry is smoothed. The mold body was demolded when no ethanol liquid escaped, and the ethanol solvent was removed in a ventilating chamber at 45 ° C to obtain a ruthenium sap.

The dried green body is placed in a sintering furnace, heated to 550 ° C at a temperature increase rate of 60 ° C / h, and the organic matter such as a rheological agent in the green body is decomposed and vaporized, and heated to 1100 at a heating rate of 200 ° C / h. The temperature was °C, then heated to a temperature of 1400 ° C at a heating rate of 50 ° C / h, and kept at this temperature for 2 h, and cooled to room temperature with a furnace to obtain a magnesia-based niobium blank.

The magnesium oxide based ruthenium blank is placed in an aluminum sol, vacuum impregnated at a vacuum of 0.03 MPa for 30 min, and baked in an oven at 120 ° C ± 10 ° C for 24 hours, and then repeated twice as described above; On the grinding machine, the surface is polished with aluminum sol as cooling liquid, and then baked in an oven at 120 °C ± 10 °C for 24 hours. Finally, the surface-polished dried enamel blank is subjected to high-temperature secondary sintering, and the secondary sintering process is The mixture was heated to 1,100 ° C at a temperature increase rate of 200 ° C / h, then heated to 1400 ° C at a temperature increase rate of 50 ° C / h, and kept at this temperature for 2 h, and cooled to room temperature with a furnace to obtain a magnesia-based niobium blank.

Example 4

According to the nanometer iron oxide, the mass percentage of the ceramic powder is 1.0%, the nano zinc oxide is 0.5%, the magnesium oxide whisker is 2%, and the rest is the ratio of the light burned magnesium oxide, and the nanometer iron oxide and the particle having the particle diameter of 60 nm are used. Nano-zinc oxide with a diameter of 20 nm, commercial magnesium oxide whiskers (with a diameter of 2 μm to 5 μm, length of 200 μm to 1000 μm) and light-burned magnesium oxide powder with a particle size of 300 mesh (medium diameter d ₅₀ of 48 μm) Ceramic powder; mixed rheological agent according to the ratio of polyvinyl butyral: hydroxypropyl methylcellulose: hydroxyethyl cellulose in a mass ratio of 5:2:3.

According to the mass percentage, the nano-alumina sol with a solid content of 20% was 25%, the rheological agent was 1.0%, and the rest was made of ceramic powder. Firstly, the lightly burned magnesia powder is added to the ball mill tank according to the ratio, and the nano aluminum sol, the nano iron oxide, the nano zinc oxide, the magnesium oxide whisker, the rheological agent and the appropriate amount of absolute ethanol are mixed and sonicated for 45 minutes. The nano-iron oxide, nano-zinc oxide and magnesium oxide whiskers are fully dispersed and added to the ball-milling tank, and then the corundum balls are added in a ratio of 2:1 of the ball-to-ball ratio, and ball-milled at 100 rpm for 3 hours to obtain a solid content of 70%. Ceramic slurry.

The dried green body is placed in a sintering furnace, heated to 550 ° C at a temperature increase rate of 60 ° C / h, and the organic matter such as a rheological agent in the green body is decomposed and vaporized, and heated to 1100 at a heating rate of 200 ° C / h. The temperature was °C, then heated to a temperature of 1450 ° C at a temperature increase rate of 50 ° C / h, and kept at this temperature for 2 h, and cooled to room temperature with a furnace to obtain a magnesia-based niobium blank.

The magnesium oxide based ruthenium blank is placed in an aluminum sol, vacuum impregnated at a vacuum of 0.04 MPa for 30 min, and baked in an oven at 120 ° C ± 10 ° C for 24 hours, and then repeated twice as described above; On the grinding machine, the surface is polished with aluminum sol as cooling liquid, and then baked in an oven at 120 °C ± 10 °C for 24 hours. Finally, the surface-polished dried enamel blank is subjected to high-temperature secondary sintering, and the secondary sintering process is The mixture was heated to 1,100 ° C at a heating rate of 200 ° C / h, then heated to 1,450 ° C at a heating rate of 50 ° C / h, and kept at this temperature for 2 h, and cooled to room temperature with a furnace to obtain a magnesia-based niobium blank.

In the above examples, the prepared magnesia-based niobium has excellent thermal shock resistance and strength, and no cracking is observed when it is cooled 100 times in air at 1000 ° C; the normal temperature crushing strength of the sintered crucible is not less than 150 MPa.

The above embodiments are not intended to limit the invention in any way, and all the technical solutions obtained by means of equivalent replacement or equivalent transformation fall within the protection scope of the present invention.

Claims

In-situ synthesis of spinel-enhanced magnesia-based bismuth by magnesium oxide whisker, characterized in that a light-burned magnesia ceramic slurry containing nano-iron oxide, nano-zinc oxide and magnesia whiskers is grouted in a plaster mold Molding, drying and sintering.
A preparation method of in-situ synthesis of spinel-reinforced magnesia-based bismuth by magnesium oxide whisker, characterized in that the method comprises the following steps:

(1) According to the mass percentage, 15% to 25% nano-alumina sol, 0.8% to 1.5% rheological agent, and the rest are magnesium oxide ceramic powder containing nano-titanium dioxide sintering aid, and then added with anhydrous ethanol. Forming a ceramic slurry having a solid content of 65% to 75%; the rheological agent is a mixture of polyvinyl butyral and a cellulose ether, wherein the polyvinyl butyral is 50% of the mass of the rheological agent %, the cellulose ether is one of industrial hydroxypropylmethylcellulose and hydroxyethylcellulose or a mixture thereof; the ceramic powder is nanometer iron oxide, nano zinc oxide, magnesium oxide whisker and Lightly burning a mixture of magnesium oxide;

(2) casting the ceramic slurry into the gypsum mold by the grouting method, demolding, and removing the ethanol solvent in the ventilating chamber at 40 ° C to 50 ° C to obtain the eucalyptus blank;

(3) placing the dried alfalfa blank into a sintering furnace, heating to a temperature of 1350 ° C to 1550 ° C for high temperature sintering, and cooling to room temperature to obtain a magnesia based crucible;

(4) The magnesium oxide based ruthenium blank is vacuum impregnated in an aluminum sol, and then subjected to surface buffing treatment. After drying, it is subjected to high temperature secondary sintering at a temperature of 1350 ° C to 1550 ° C, and is oxidized by cooling to room temperature with the furnace. Magnesium based bismuth.
The method for preparing a spinel-enhanced magnesium oxide-based bismuth according to claim 2, wherein the nano-alumina sol has a solid content of 20% to 25%, and the PH value thereof ≥4.
The method for preparing a spinel-reinforced magnesia-based bismuth according to claim 2, wherein the nano-iron oxide accounts for 1% to 2% of the mass of the ceramic powder. The nano zinc oxide accounts for 0.5% to 1% of the mass of the ceramic powder, and the magnesium oxide whisker accounts for 1.5% to 2.5% of the mass of the ceramic powder, and the rest is light burned magnesium oxide.
The method for preparing a spinel-reinforced magnesia-based bismuth according to claim 2, wherein the nano-iron oxide has a particle diameter of 30 nm to 60 nm, and the nano-zinc oxide The particle size is 20 nm to 30 nm, and the magnesium oxide whisker is an industrial product having a diameter of 2 μm to 5 μm and a length of 200 μm to 1000 μm, and the light burned magnesium oxide powder has a particle diameter of 250 mesh to 500 mesh.
The method for preparing a spinel-reinforced magnesia-based bismuth according to claim 4, wherein the ceramic slurry is prepared by: calcining magnesium oxide powder according to a ratio The material is added into a ball mill tank, and the nano aluminum sol, nano iron oxide, nano zinc oxide, magnesium oxide whisker, rheological agent and absolute ethanol are mixed and sonicated for 30 min to 60 min to make nano iron oxide, nano zinc oxide and magnesium oxide. The whiskers are fully dispersed and added to the ball mill tank, and then the corundum balls are added in a ratio of 2:1 of the ball to the ball, and ball-milled at 60-120 rpm for 2 to 4 hours to obtain a uniform mixture.
The method for preparing a spinel-reinforced magnesia-based niobium in situ by using a magnesium oxide whisker according to claim 2, wherein the preparation method of the niobium billet is: injecting the ceramic slurry into the plaster mold quickly It is placed on a vibration molding machine to form a vibration. When the slurry is completely filled with the mold, the surface of the slurry is uniformly sprayed to stop the vibration, and the surface of the slurry is smoothed. The surface of the green body is released without ethanol liquid, and the mold is released at 40 ° C to 50 ° C. The °C ventilator is obtained by removing the ethanol solvent.
The method for preparing a spinel-reinforced magnesia-based bismuth according to claim 2, wherein in the step (3), the sintering process is: 60 ° C / The heating rate of h is heated to 550 ° C, and the organic matter in the green body is decomposed and vaporized, heated to a temperature of 1100 ° C at a heating rate of 200 ° C / h, and then heated to a temperature of 1350 ° C to 1550 ° C at a heating rate of 50 ° C / h. The temperature is maintained at this temperature for 2 to 3 hours.
The method for preparing a spinel-reinforced magnesia-based niobium in situ by synthesizing a magnesia whisker according to claim 2, wherein the method for vacuum impregnation of the magnesia-based niobium billet in an aluminum sol is: The magnesia-based bismuth blank is placed in an aluminum sol, vacuum impregnated for 30 min under a vacuum of 0.02 MPa to 0.05 MPa, and baked in an oven at 120 ° C ± 10 ° C for 24 hours, and then repeated twice as described above. Then, the surface is polished by using an aluminum sol as a cooling liquid on a grinding machine, and then baked in an oven at 120 ° C ± 10 ° C for 24 hours; finally, the surface-polished dried enamel blank is subjected to high-temperature secondary sintering, the second The secondary sintering process is: heating to 1100 ° C at a heating rate of 200 ° C / h, then heating to 1350 ° C ~ 1550 ° C at a heating rate of 50 ° C / h, and holding at this temperature for 2 ~ 3h.